Basically they found a way to pack more cells into the same physical space. But this is the limit for this pack dimension using 18650 cells. Going forward Tesla will have to use the new 2170 cell.

By the way, both Faraday Future and Lucid motors are using 21700 cell formats in their batteries. That's how they're getting up to 130kWh in their packs.
Remember, both of those companies have ex Tesla battery people and engineers so they already knew Tesla knew was going to the 21700 cell eventually, they just went straight to that size.

Expect Tesla to reach those levels in the future too.

Note: Please do not post any of his pictures on our forum. Jason has proven a good tinkerer but is rather trigger happy with legal threats.